My instinct would be to use a ViewContext. Here's why. I believe that CAB events should be used in a fire-and-forget manner to communicate something of possible interest to unknown subscribers. Here you have a collaboration between two parts. They may be loosely coupled (and not know each other) but they are the only two parties to the conversation.
The ViewContext was invented to facilitiate conversation among loosely-coupled close collaborators. That's what your scenario suggests to me.
I don't know of a specific implementation in Cabana for this scenario. I don't know if ViewContext is the best answer for your case either but it the place I would look first.